Cellulose Fiber Insulation

Yesterday I did a one year inspection on a home with cellulose fiber blown
into the attic space. The tag said 8.5" but I measured 6-7" consistently
over the entire attic space. I know there is some compaction over time, do
you think there was originally 8.5" installed.
Of course the builder is going to argue. Does anyone know of a document or link which discusses compaction of insulation and might give typical amounts.


If you’ve got 6-7" of blown-in cellulose, do yourself a favor…Let it go.

Cellulose insulation has an R-Value of 3.4 per inch. That will still give your client an R-value of 20.4 to 23.8. I’m not sure what your area requires, but adding an additional 2" of cellulose is a ridiculous recommendation.

If I find cellulose to be approx. 6-8 inches in a typical attic, I don’t recommend additional.

You might check your energy code for the area you live in, if the is one. Ours requires R-38, for new construction, in the attic so I recommend additional insulation if less than that but I don’t make a big deal out of it. Really, there are a lot of variables on the cost effectiveness.

Many studies recommend around R-48 for energy conservation.

If I was building new I would want the higher value.

If it is a new house the minimum is R32. So it would not be acceptable.

Hi David
In this case adding an additional 2" of cellulose isn’t ridiculous because my client already paid for it and didn’t get it. Minimum code in my area is 8.5" so he was shorted about 20%. The expected settlement is in the order of 12% so I don’t believe he ever received the full 8.5".
In any case, it doesn’t hurt to ask the builder, even if he says no way.